Ah, for fucks sake. I just checked this and have tons of messages. I'm a promoter Facebook! Of course I want to get these messages and why is there an "other" folder for an already existing "other" folder?!
"Users have discovered hundreds of messages locked in a hidden inbox within Facebook’s messaging system.The inbox, accessible on the web or Facebook Messenger apps for smartphones and tablets, is part of Facebook’s filtering system, designed to catch spam and other unwanted messages.However, users, including myself and others within the Guardian, have discovered their “filtered” inbox full of legitimate messages that never made it to the main inbox or Messenger app."
To learn how to access these messages, check here.